如何在不修改以前的文本的情况下更改WPF RichTextBox中的FontFamily

When you use the FontFamily property of the RichTextBox it changes the FontFamily of the whole content inside the FlowDocument. The same way you can Execute a command like EditingCommands.ToggleBold, where it only changes the word under the caret or just the new text to be written, there should be a way to do the same thing with the FontsFamilies, and Color.When you use the FontFamily property of the Ric